Effect of karstic collapse column on hydrogeochemistry of produced water from coalbed methane wells in Sijiazhuang mine field

In order to study the hydrogeochemistry characteristics of produced water from coalbed methane (CBM) wells in karstic collapse column (KCC) area, Sijiazhuang block, the salinity, type and ion concentration of Sijiazhuang coalbed methane produced water (CMPW) were tested and analyzed with hydrochemistry and one-way variance statistics method. The analyses are useful for CBM exploration and development in KCC areas. The average salinity of CMPW samples is 1 484 mg/L, belonging to saline groundwater with HCO₃-Na type. The CMPW in the north has higher salinity than that in the south either in April or in August. KCCs were and are developed in the north and may increase the evaporation of the groundwater. The salinity of CMPW in August is higher than that in April, slightly increasing with CBM production processing, indicating that the groundwater does not get recharged on time in the process. The Na⁺ concentrations of samples under different regional tectonic regimes are significantly different, of which sample No. 282 occur on a synclinal axis and near a KCC, which may result in the highest Na⁺ concentration, with a mean of 462 mg/L.